1. Field of the Invention
The present invention relates to a sheet feeding apparatus for use in an image forming apparatus such as a copying machine or a printer, and an image forming apparatus using the sheet feeding apparatus, and more particularly, to a sheet feeding apparatus which is able to stably feed even envelopes.
2. Description of the Related Art
In automatic sheet feeding for conventional copying machines and printers, a stack of sheets is fed and separated one by one by a delivery roller or the like.
Various types of sheet separation methods have been proposed. One of the proposed methods adopts a retard separation mechanism composed of a feed roller for rotating in a direction to feed sheets and a retard roller for rotating in a reverse direction to return the sheets.
Although a popular type of printer separates and feeds cut sheets of so-called plain paper one by one and records images thereon, the number of printers, which are able to separate and feed a plurality of envelopes as sheets, one by one, and to automatically print the names of addressees and senders, has increased in recent years.
However, envelopes are provided with a sealing flap as distinct from cut sheets, and two sheets lie one over the other at the flap of a single envelope. Therefore, in separation of the envelope particularly by the retard separation mechanism, the retard separation mechanism performs a separating operation at the flap of the envelope, which sometimes buckles the leading end of the envelope and causes sheet jam.